In numerous mass-produced calibres, the balance spring stud, forming the external point of attachment of the balance spring, is clipped to a stud-holder, which is a flat, stamped part.
In high end productions, the balance spring stud is screwed into a stud-holder which is a machined component. The retaining screw then works between the screw foot and threads. The head is never locked, which causes frequent breakage, as a result of the torsion stresses experienced when the foot is locked onto the balance spring stud and when the operator continues to turn the screw.
CH Patent Application No 332548A in the name of PARECHOC SA discloses a device for regulating the active length of a balance spring, wherein the end of the balance spring is secured without a stud, by a device which clamps the balance spring directly, without the intermediary of a balance spring stud. A component called a “balance spring holder” and a component called a “bent plate” are necessary to confine, together, the balance spring. This bent plate, which is an independent component, cannot be equated with a balance spring stud. A screw is used to lock the balance spring. A first elastic strip is used to determine the active length of the balance spring. The bent plate pushes a second elastic strip onto said first elastic strip to prevent it from moving in an inopportune manner. This mechanism does not allow for the insertion and release of a unit carrying the balance spring, simply by the elastic effect of a strip.
EP Patent Application No 2290477A1 in the name of GLASHÜTTE UHRENBETRIEB describes a stud-holder which includes an inner thread for securing the stud retaining screw, which cooperates with a recess in said stud, over one part of the thickness of the stud. The dividing wall which carries the internal thread receiving the screw is a rigid wall. This construction uses a anti-friction pad able to be added between the stud and the balance spring in order to modify the point of attachment. Therefore, this is again a system for adjusting the active length of the balance spring.
In both cases, it is the actual balance spring which is clamped. This cannot work with a silicon balance spring which cannot withstand torsion or compression stresses.